The present invention relates to combined cycle plants and more particularly to protective shutdown systems for such plants.
In the combined cycle plants presently supplied to electric power companies, a pair of gas turbines generate hot exhaust gas which is used to produce steam in a pair of heat recovery steam generators. The steam drives a steam turbine and in turn a generator is driven by each of the gas and steam turbines to produce the plant power. An afterburner may or may not be associated with each gas turbine to provide supplemental heating of the turbine exhaust gas.
Various contingencies may occur which require that one of the gas turbines or the entire plant be shut down. A shutdown system is arranged to respond to the occurrence of predetermined plant events and cause a partial or full plant shutdown.
In plants having a dual liquid fuel system, and specifically where one fuel is an ignition fuel requiring no special processing and a heavy or highly volatile fuel requiring special processing, a plant shutdown can result in coagulation of heavy fuels in the fuel lines, dangerous leaking of highly volatile fuels into the hot combustion path, or closing of the burner nozzles after flameoff. Manual prestart preparation of the fuel system is then required before restart of the plant. It is desirable that shutdowns in such plants be enabled to occur safely and orderly such that restarts can occur immediately without requirement for special prestart fuel preparation procedures.